1. Field of the Invention
The present invention relates to an optical scanning device and an image forming apparatus, and more particularly to an optical scanning device for scanning a photoreceptor surface with beams and to an image forming apparatus having the optical scanning device.
2. Description of Related Art
A scanning device disclosed by Japanese Patent Laid-Open Publication No. 2002-40350 is well known as a conventional optical scanning device. This scanning device has a surface-emitting laser, a rotative polygon mirror, a half mirror, a light receiving element and a control section, and this device is adapted to scan a photosensitive drum with a plurality of beams concurrently.
The surface-emitting laser emits a plurality of beams. The rotative polygon mirror deflects the plurality of beams to permit the beams to be scanned on the photosensitive drum. The half mirror is located between the surface-emitting laser and the rotative polygon mirror and reflects part of each of the beams. The light receiving element receives the beams reflected from the half mirror and outputs signals with voltages corresponding to the light intensities of the reflected beams. The control section controls the surface-emitting laser based on the signals outputted from the light receiving element. This permits feedback control of the output of the surface-emitting laser.
In the optical scanning device disclosed by Japanese Patent Laid-Open Publication No. 2002-40350, each of the plurality of beams is partly reflected from the half mirror to the light receiving element. Therefore, the light intensity of each beam deflected by the rotative polygon mirror is lower than the light intensity immediately after the beam was emitted from the surface-emitting laser by the light intensity reflected from the half mirror. Thus, the light intensity of the beam deflected by the rotative polygon mirror is reduced, and the light intensity that is used as the base of generation of a main-scanning synchronizing signal is reduced. Consequently, the light intensity used for generation of a main-scanning synchronizing signal is insufficient, and it may be impossible to generate a main-scanning synchronizing signal accurately.